Effect of Oxamyl Treatment of Potato Seed Pieces on Pratylenchus penetrans and Yield.

In the first 2 years of a 3-year (1987-89) microplot study, aqueous solutions of oxamyl (32 mg/ml) were applied to cut potato (Solanum tuberosum cv. Russet Burbank) tubers, grown in fine sandy loam infested with Pratylenchus penetrans. The seed-piece treatment alone and the seed-piece treatment followed by three foliar sprays generally reduced (P = 0.05) population densities of P. penetrans in the soil at midseason and in the soil and roots at harvest, compared to the control. In 1989, all seed pieces treated with oxamyl at 96 mg/ml or at 32, 64, and 96 mg/ml followed by a polymer sticker : water (1:4) dip failed to emerge. Only oxamyl at 64 mg/ml reduced (P = 0.05) midseason soil population densities of P. penetrans. A pre-plant soil treatment with 1,3-D reduced (P = 0.05) numbers of P. penetrans at planting each year and increased (P = 0.05) tuber yields in 1988 and 1989 compared to the control. In 1989, tuber yields from the sticker treatment and the oxamyl seed-piece treatment at 64 mg/ml were lower (P = 0.05) than those in the 1,3-D treatment and similar to those from the untreated control, possibly because of phytotoxicity. Oxamyl treatment of potato seed pieces to control P. penetrans does not appear practical for field production.